December 2019: Fixed gas fire extinguishing systems

This safety update is issued to raise awareness of potential problems that can occur with fixed gas fire extinguishing systems on vessels. The focus is on CO2 based systems, but the principles apply more broadly.

This safety update is for

  • New Zealand ship owners, operators, masters and crew
  • Maritime NZ recognised surveyors and design approvers


What is a fixed gas fire-extinguishing system?

A gaseous substance (often CO2) in a cylinder separate from, but connected to, a protected space is used to fight a fire. Commonly fixed systems are installed for engine rooms and pump rooms.

After air vents are closed and the area sealed, the gas is released in bulk quantity to flood the protected space and smother the fire.

There are alternatives to CO2, some of which can be used in occupied places (e.g. FM200 copyrighted by DuPont – actual chemical is HFC 227ea).


What are the safety risks?

Not air tight

A gas based fire fighting system is ineffective if the space being protected cannot be fully closed down. Even though CO2 is heavier than air it will be less effective if external air can feed the fire.

Flaps and other air pathways need to be closed BEFORE the fire suppressor is released.

Unknown structural design issues

Changes to a vessel (e.g. new wiring, pipes and cabinets) can affect the effectiveness of fire suppression by inadvertently creating new air pathways.

Crew not familiar with the system

Training, signage and clear roles are important. Knowing how the system works supports the right actions – both before and during a fire.


Carbon dioxide (CO2), has very little cooling effect, so there is a danger of re-ignition.

Wellbeing of people

High concentrations of CO2 can be toxic to people. Accidental release of CO2 can result in death.


Actions to take

Good Design

Under the Maritime Rules you are required to:

  • make sure the means of control is readily accessible, simple to operate and grouped together in as few locations as possible [Maritime Rule 42B.20(7)].
  • minimise the chances of access to control systems being cut off by fire [Maritime Rule 42B.20(7)(c)]
  • provide the ability to close all openings that may admit air or allow gas to escape [Maritime Rule 42B.20(4)]
  • for CO2 systems, install two clearly marked separate controls: one to release from the storage container and a second valve to allow gas to go into the protected space [Maritime Rule 42B.21(6)].
  • The ability to test the system should be built into the design.

In addition, it is recommended that you consider the following factors prior to installation: ambient temperature changes, vibration, humidity, shock, impact, clogging and corrosion that might be expected to occur to the protected space.

Operation and maintenance

  • Follow manufacturer’s instructions for installation and maintenance of component parts.
  • Include in maintenance schedule – ISM and MOSS as appropriate. Pay special attention to the proper setting, repair and maintenance of the cylinder valves. Improperly set or maintained valves may result in unintended release of the gas which can have fatal consequences.

Know your vessel

  • Know how the fire suppression works – have drawings of all air shut-off systems and sufficient technical data and schematics to show how to test and operate the system.
  • Building joints and cable connections move over time introducing leak points.
  • Vessel maintenance and modifications may affect the integrity of the boundary of the protected space and system.
  • When any vessel construction or repair work occurs, ensure contractors understand the importance of the integrity of air tight spaces.

Signage and training

  • Clear signs to mark the position of air shut-off controls, with crew instructions.
  • Fire drills should include testing of control valves and the order of actions – use different scenarios.
  • Include fire system operation in the safety orientation for all new crew.
  • Know procedures for when/if to re-enter – check heat, listen to goose necks (steel pipes coming from the enclosed space).

Limit leakage - If the protected space leaks, the fire suppression agent will escape and/or oxygen will feed the fire before it is effectively controlled.


Contact us for more help

If you have any questions about this safety update, please contact our Wellington office.


New Zealand (toll free):
0508 225 522

Calling from outside New Zealand:
+64 4 473 0111

Tell us what you need help with and remember to include your contact details (email address and phone numbers).